Cholesterol & Plasma Membrane Terms | Biology Study Set

Cholesterol is almost all hydrocarbon. What does this mean?

It's made of mostly carbon and hydrogen.

What kind of specific chemical bond do the carbon and hydrogen atoms in cholesterol make? And does the molecule dissolve in water?

Nonpolar covalent bonds. No, the molecule is very nonpolar, which means it's hydrophobic, and does not dissolve in water.

Do we absolutely need cholesterol in our diet? Most of the cholesterol in our body is made in this organ ___________.

No, we do not require cholesterol in our diet but we do need it! Most is made in our liver.

What two lipids help make up the plasma membrane?

phospholipids and cholesterol

What function does cholesterol have in the plasma membrane?

It helps regulate the fluidity of the membrane (how well and how fast molecules move around in the membrane).

What is bile made of and where is it made?

Bile is made from cholesterol and salts. It is made in the liver.

What consumed nutrients does bile work on? How does it assist in digestion of these nutrients?

Bile works on lipids, like consumed fats. It functions by dissolving (emulsifying) the fats, like a detergent would on greasy dishes. Once dissolved, the fats can then be digested by fat-digesting enzymes.

Bile is made in one organ, but stored in a different organ. Where is bile stored?

gall bladder

Can you live without your liver? Can you live without your gall bladder?

You cannot live without your liver but you CAN live without your gall bladder.

If your gall bladder is removed, what nutrient do you have a hard time digesting, and why?

It's hard to digest fats, because the bile needed to dissolve the fats to make them accessible to digestive enzymes is not readily available.

What are you urged to avoid eating if you have your gall bladder removed, and why?

You should not eat fatty foods because you do not have an immediate supply of bile to dissolve the fats, and the fats are then not easily digested by fat-digesting enzymes.

Which vitamin is made from cholesterol?

Vitamin D

What types of hormones are made from cholesterol? Provide two examples.

Steroid hormones. Examples: the sex hormones, estradiol (estrogen) and testosterone (later we'll see also progesterone, aldosterone and cortisol).

What are the components of a phospholipid? Which part is charged, and is it positively or negatively charged?

Glycerol, 2 fatty acids and a modified phosphate group. The phosphate group is negatively charged.

Which part of a phospholipid is nonpolar (hydrophobic) and which part is polar (hydrophilic)?

The 2 fatty acid tails are nonpolar and don't like water, and the negatively charged phosphate group is polar and loves water (polar head group).

What is the main structural lipid of the plasma membrane and how is it arranged?

Phospholipids make up the plasma membrane, and they are arranged in a bilayer.

How is the bilayer of the plasma membrane arranged? Are the polar head groups facing inwards or outwards? What about the fatty acid tails?

The polar head groups face outwards toward the watery liquid, and the fatty acid tails face inwards towards each other.

The fatty acid tails of a bilayer are not happy if the bilayer is completely linear because they are exposed to water at the ends. So what must the bilayer do to make everyone happy?

The bilayer forms a circle.

Besides phospholipids and cholesterol, what other functional molecules are present in the plasma membrane?

proteins

Can the components of the plasma membrane move around at all? What constraints do they have?

Yes, the components of the plasma membrane can move freely laterally, but are not free to flip-flop.

What are the two main types of membrane proteins?

Integral membrane proteins and peripheral membrane proteins.

Which of the two general types of membrane proteins are embedded in the membrane?

integral proteins

Which of the two general types of membrane proteins are loosely attached to the membrane?

peripheral proteins

Which are more permeable to the plasma membrane, nonpolar molecules or polar molecules?

nonpolar molecules

Which type of molecule dissolves well in water, a nonpolar molecule or a polar molecule?

a polar molecule (especially if charged)

Very small polar molecules are able to slowly pass through the plasma membrane, as long as they are not ___________.

charged

Most polar molecules (are/are not) not freely permeable to the plasma membrane.

They are NOT freely permeable to the plasma membrane (unless they are only a few atoms and are uncharged).

Ions like sodium (are/are not) freely permeable to the plasma membrane

are NOT

For the following substances, indicate whether the substance is freely permeable to the plasma membrane or not. This does not say whether the substance crosses FAST, just that it is permeable.

~ a sodium ion

~ CH4 (methane)

~ glucose

~ O2 (oxygen)

~ testosterone (a lipid which is a steroid hormone)

~ starch (polymer of glucose)

~ water

~ a sodium ion - NOT permeable (tiny, but charged)

~ CH4 (methane) - permeable (nonpolar covalent bonds)

~ glucose - NOT permeable (polar and too large)

~ O2 (oxygen) - permeable (nonpolar covalent bond)

~ testosterone (a lipid steroid hormone) - permeable

~ starch (polymer of glucose) - NOT permeable (huge!)

~ water - permeable (polar, but tiny and uncharged)

Which way do substances naturally go, from high concentration to low concentration, or from low concentration to high concentration?

Substances flow naturally from high concentration to low concentration.

What are the differences in energy requirements between passive transport and active transport?

Passive transport does not require energy, but active transport does.

Why are there energy requirement differences between passive transport and active transport?

In passive transport, substances are traveling from high concentration to low concentration while in active transport, the reverse is true.

What is the energy currency for all living cells?

ATP

What are the three types of passive transport?

Simple diffusion, osmosis, and facilitated diffusion.

A particle dissolved in a liquid is also known as a __________.

solute

The liquid dissolving a particle is also known as the _______.

solvent

The solvent in biology is almost always _______.

water

If a solute is moving down its concentration gradient , and the solute is freely permeable to the membrane, what type of passive transport are we talking about?

simple diffusion

If a solute is moving across a membrane, down its concentration gradient, and the solute is NOT freely permeable to the membrane, what type of passive transport are we talking about?

facilitated diffusion

In simple diffusion if there are two or more solutes, each solute goes down its own concentration gradient. Once the solutes are at an equilibrium, does movement stop? Explain.

No, movement never stops. However, there is no net movement of solutes overall. This is called a dynamic equilibrium.

Movement of water across a membrane , down its own gradient is known as ________

osmosis

Under what conditions can simple diffusion and osmosis occur at the same time?

If the membrane is permeable to both the solute and water (solvent), simple diffusion and osmosis will occur at the same time.

What is tonicity?

Tonicity is defined as the relative concentration of solutes in a solution.

When we are talking about tonicity, what specific requirements must there be about the membrane?

The membrane must be permeable to water, but not to the solute.

When you see the word tonicity, what should you replace the word tonic with?

solute concentration

What is a definition for solute concentration?

Solute concentration is the number of solutes in a solution of a particular volume. If we are measuring the volume in milliliters, then it's the # of solutes per milliliter (solutes/ml).

If we are comparing two environments, the hypertonic environment is the environment with the _________ solute concentration and _________ water concentration.

higher; lower

If we are comparing two environments, the environment with a lower solute concentration is the ____________ environment. This environment has a ____________ water concentration than the other environment.

hypotonic; higher

If two environments have equal solute concentrations, they are considered to be __________.

isotonic

Which way does water naturally flow, from a hypertonic solution to a hypotonic solution, or vice versa?

Water naturally flows from a hypotonic solution to a hypertonic solution.

If you place an animal cell in a very hypotonic environment, what will happen to it?

Water will rush into the cell, and the cell will swell and may actually burst (lyse).

Which type of environment do animal cells prefer to live in, hypertonic, hypotonic, or isotonic?

isotonic

Which type of environment do plants prefer to live in, hypertonic, hypotonic, or isotonic?

hypotonic

What prevents a plant cell from exploding in a hypotonic environment?

The presence of a rigid cell wall. The cell wall allows water to enter the cell until the cell membrane expands up against the cell wall, and then no more water enters.

What would happen if you put a plant cell in a very salty solution? A salty solution is very hypertonic to the inside of the cell.

The cell would lose water and shrivel. This is known as plasmolysis.

Protists like the paramecium require environments that are isotonic. However, they live in rather hypotonic pond water. How do they prevent their cells from exploding?

They have internal organelles called contractile vacuoles that continuously pump out excess water that has entered the cell.

Why is assistance required in facilitated diffusion?

The solute is not freely permeable to the cell (although it is still trying to go from high to low concentration).

What type of macromolecule assists transport of solutes during facilitated diffusion? Where in the cell does this facilitating molecule exist?

The facilitators for transport are proteins that are embedded in the plasma membrane (integral proteins)

Does facilitated diffusion require energy? Why or why not?

No, facilitated diffusion does not require energy! This is because in facilitated diffusion the solute is attempting to move from high concentration to low concentration. It is still a type of passive transport!

What are the two main types of transport proteins in facilitated diffusion?

channels and carriers

Channels and carriers are (highly specific/not specific) for the solute they transport across the membrane

highly specific

What type of solute is usually transported by a channel?

Ions, like Na+ or K+ are usually transported by channels.

A channel that is open all the time is known as a ______ channel.

leak

Gated channels provide more regulation than channels that are open all the time. Provide two common examples of stimuli that can open or close a gate.

1) a change in electrical voltage across the membrane (voltage-gated channels)

2) a specific molecule that binds to the gate (ligand-gated channels)

3) also have channels that can open by a physical stimulus like pressure.

The movement of ions (e.g. Na+ or K+) down a membrane is also known as _____________ (flow of ions)

electricity

If a hormone binds to a gate and opens up a channel, the channel is called a __________-gated channel.

ligand

Which type of transporter contains a hinge that alternate between two different conformations to open and close? (hint: it looks like a pac-man)

a carrier

What type of transporter does the molecule glucose use to get into the cell?

glucose uses a carrier protein

Some individuals with Type 2 diabetes are unable to get their glucose carriers to the plasma membrane. What happens to the glucose in the blood in these individuals?

Since the carriers cannot get to the plasma membrane, they cannot carry glucose into the cell, and glucose levels remain high in the blood.

Which of the following would not be permeable at all to the plasma membrane without a transporter protein?

1) water

2) estrogen (a very nonpolar steroid hormone)

3) N2 (two nitrogen atoms covalently bound to each other)

4) Cl- (chloride ion)

5) octane (hydrocarbon with all carbon and hydrogen bound covalently to each other)

All of them are either nonpolar (permeable) or very tiny and uncharged (water) except Cl-. Even though the chloride ion (Cl-) is tiny, it is charged, which makes it completely impermeable to the membrane unless it is transported by a membrane protein (a channel). Only the Cl- would be completely impermeable without a transporter.

If you are transporting solutes from low concentration to high concentration, you are using a type of transport called _________ . This type of transport (requires/does not require) energy .

active transport; does require energy

The transporters that perform active transport are called _______, and they (do/do not) require ATP.

pumps; do require ATP

How many phosphate groups does ATP have?

3 phosphate groups

When ATP is hydrolyzed, the products are ________ and ________ plus a lot of energy.

ADP and a phosphate group

The energy stored in ATP is due to the bonds between the _________ groups

phosphate

The bond that is broken in ATP is a very (stable/unstable) bond, which means that it stores (a lot of/very little) energy.

unstable; a lot of energy

What does an ATPase do?

It catalyzes the hydrolysis (break down) of ATP, releasing energy that can be used to perform work.

Do we normally have a lot more sodium on the inside (cytoplasm) or on the outside of a resting cell?

outside

Do we normally have a lot more potassium on the inside (cytoplasm) or on the outside of a resting cell?

inside

The sodium potassium pump transports sodium and potassium against their concentration gradients. It pumps_____ sodium ions (in/out), and ____ potassium ions (in/out).

It pumps 3 sodium ions OUT and 2 potassium ions IN.

Besides maintaining proper sodium and potassium levels in the cell, what else does the sodium potassium pump do in animal cells?

The sodium potassium pump also helps an animal cell maintain isotonicity.

How does an animal cell prevent excess water molecules from entering the cell when solutes are taken up by the cell?

When a solute enters the cell, water would normally follow by osmosis. However, every time a solute enters, the sodium potassium pump goes through a round of pumping. It pumps a net solute out, which prevents water from being driven into the cell.

An integral membrane protein which has a portion on the outside that can interact with a ligand, and a portion on the inside that can interact with other proteins to generate a response is a __________.

receptor

Plasma membrane receptors that work through signal transduction (do/do not) carry their ligand into the cell.

do not

Instead, they bind the ligand and the receptor changes shape, interacting with another membrane protein which kicks off a cascade of events.

Epinephrine is a hormone that binds to a plasma membrane receptor and stimulates a number of events inside the cell. Epinephrine never actually enters the cell, so its receptor is working through a mechanism called ________ _________.

signal transduction

A plasma membrane receptor which carries its ligand into the cell is working through a mechanism called ________- _________ _________

receptor-mediated endocytosis

Is cholesterol carried into the cell using signal transduction or receptor-mediated endocytosis?

receptor-mediated endocytosis

The so-called "bad" cholesterol is actually cholesterol being carried by a lipoprotein carrier. This carrier is called ___________.

LDL

Which of the following would be MOST likely to diffuse through a plasma membrane easiest without the help of a transport protein?

- large, polar molecule

- small, polar molecule

- small nonpolar molecule

- very small ion (charged particle)

- large nonpolar molecule

small, nonpolar molecule

You are given a special balloon that is permeable to water but not sucrose. The balloon is filled with a solution of 80% sucrose and 20% water and is immersed in a beaker containing a solution of 30% sucrose and 70% water. Will sucrose enter/leave the balloon? Will water enter/leave the balloon?

Sucrose will not enter or leave the balloon (it is not permeable), but there will be a net movement of water into the balloon because there is a lower concentration of water inside the balloon than outside the balloon.

When you are using the terms hypertonic, hypotonic and isotonic, you must be comparing two solutions! Therefore, if two solutions are isotonic, there will be ______ net flow of water. On the other hand, water will move from a _______ to a _______ solution.

If two solutions are isotonic, there will be NO net flow of water. On the other hand, water will move from a HYPOTONIC to a HYPERTONIC solution.

If you open a bottle of ammonia, the vaporized ammonia will move out of the bottle into the air. The process by which this occurs is called __________________

simple diffusion

What type of transport is used to get glucose into our cells? (simple diffusion, active transport, osmosis, facilitated diffusion). What specific hormone is also required for the uptake of glucose? ________

facilitated diffusion; insulin